test: fix cli mocks, add pytest config and coverage gaps

- tests/test_cli.py: fix 26 fetch_issues_with_spent_time mocks to return
  3-element tuples (issue, hours, activities) matching the real signature
- pyproject.toml: add [tool.pytest.ini_options] with testpaths and
  pythonpath so bare pytest works
- tests/test_client.py: add pagination test (>100 time entries arriving
  in pages, hours aggregated across all pages)
- tests/test_formatters.py: add structural tests — XLSX full header row
  and grand total row via openpyxl, HTML thead with all columns and
  tbody row count
- add strict xfail trap-tests for known bugs: #58 (naive created_on vs
  aware dedup cutoff TypeError) and #59 (parse_date_range rejects
  datetime range from dynamic+datetime period)

Closes #67

pyproject.toml

@@ -45,6 +45,10 @@ include = ["redmine_reporter*"]
 [tool.setuptools.package-data]
 "redmine_reporter" = ["templates/template.odt"]
 
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["."]
+
 [tool.mypy]
 warn_unused_configs = true